Co-pyrolysis process for forming carbonized composite bodies

ABSTRACT

A co-pyrolysis process is disclosed for forming carbonized composite bodies in which co-pyrolysis of organic fibrous and matrix components is effected during initial pyrolysis. Improved interfacial bonding of composite bodies is achieved by combining fibrous precursors, or reinforcements with a controlled pre-shrink state, with an appropriate matrix to insure shrinkage matching during processing. Processing involves the heat treatment of an organic fibrous component, impregnation of the heat treated fibrous component with a resinous binder, forming a layup of the resin impregnated fibrous component, subjecting the layup to molding and curing cycles to form a laminate, pyrolysis of the laminate, and post-pyrolysis heat treatment of the pyrolized laminate.

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured and used by or forthe Government of the United States for all governmental purposeswithout the payment of any royalty.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a co-pyrolysis process forforming carbonized composite bodies in which co-pyrolysis of organicfibrous and matrix components is effected during initial pyrolization.More particularly, the invention relates to a co-pyrolysis process forimproving interfacial bonding of composite bodies by combining fibrousprecursors, or reinforcements with a controlled pre-shrink state, withan appropriate matrix to insure shrinkage matching during processing.

2. Description of the Prior Art

Carbonized composite bodies, especially reinforced carbon-carboncomposites, are subjected to many modern industrial applications,particularly in the fields of aerospace and aviation. As noted in U.S.Pat. No. 4,500,602, reinforced carbon-carbon composites that aregenerally constructed of fibers and bound by carbon matrix produce amaterial having excellent structural properties. The precursors forcarbonaceous fibers are polyacrylonitrile, rayon, or pitch based fiberswhile the carbon-carbon impregnation materials are phenolic, furfuryl orpitch based materials. However, reinforced carbon-carbon composites aresubject to degradation in high temperature oxygen environments unless,in accordance with the teachings of the aforesaid disclosure aprotective coating is provided which comprises a first coating layer ofsilicon carbide and a second layer of sputtered zirconium oxide.

A method of fabricating carbon composites involving both resin andchemical vapor deposition (C.V.D.) steps is disclosed in U.S. Pat. No.4,490,201 whereby a suitable carbonaceous binder, such as phenolicresin, polyimide resin, or a like material is applied in a limitedamount to a partially carbonized fibrous material, such aspolyacrylonitrile, wool, rayon, or pitch felt prior to pyrolization andC.V.D. of pyrolytic carbon densification steps. A major disadvantage ofthe C.V.D. method is that some form of expensive and bulky shapingfixture is required to hold the substrate materials in the desiredconfiguration until sufficient pyrolytic carbon has been deposited torigidize the fibrous structure.

Other patents of general interest are U.S. Pat. Nos. 4,234,650;4,029,829; 3,991,248; 3,462,340; and 3,233,014.

SUMMARY OF THE INVENTION

The present invention provides a method for forming structuralcarbon-carbon composites with significantly improved interfacialbonding. Improvement of such interfacial bonding was achieved bycombining fibrous precursors, or reinforcements with a controlledpre-shrink state, with an appropriate matrix to insure shrinkagematching during processing. Fibrous precursors that were subjected to aheat treatment process prior to an application of an appropriate matrixforming resinous component emitted fewer volatiles during subsequentpyrolysis. The flexure strength of bodies having pretreated fibrousprecursors that were subject to a post-pyrolysis heat treatment processincreased significantly to in excess of 50,000 psi eliminating the needfor a densification process.

In summary, improved composites were produced by using a fibrouscomponent along with an organic resinous binder. Briefly, the processcomprises the heat treatment of the fibrous component, impregnation ofthe heat treated fibrous component with a resinous binder, forming pliesof the resin impregnated fibrous component in a layup, subjecting thelayup to molding and curing cycles to form a laminate, pyrolysis of thelaminate, and a post-pyrolysis heat treatment of the pyrolized laminate.

It is therefore an object of the present invention to provide aco-pyrolysis process for forming structural carbon-carbon compositebodies of useful strength, structural integrity, and larger size thannormally produced by prior art processes.

It is a further object of the invention to provide nondensifiedcomposite bodies of acceptable strength in comparison to othercarbonization processes that utilize multiple densification steps.

Still another object of the invention is to provide a co-pyrolysisprocess for forming carbonized composite bodies with shorter processingtime by omitting multiple re-impregnation and curing cycles.

Yet another object of the invention is to provide a co-pyrolysis processfor forming carbonized composite bodies in which co-pyrolysis of organicfibrous and matrix components is effected during initial pyrolization.

Still a further object of the invention is to provide a co-pyrolysisprocess for forming carbonized composite bodies with significantlyimproved interfacial bonding.

Achievement of the above and other objects and advantages which will beapparent from a reading of the following disclosure and the overcomingof the shortcomings and disadvantages of the prior art processes haveproceeded in the case of the present invention from the discovery by thepresent inventors that composite bodies with significantly improvedinterfacial bonding may be achieved by combining fibrous precursors, orreinforcements having a controlled pre-shrink state, with an appropriatematrix to insure shrinkage matching during processing and that compositebodies with significantly increased flexure strength may be achieved byheat treating pyrolyzed composites.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with an embodiment of the present invention, woven clothof an organic fibrous material such as Kynol 2400 (a phenolic-basedfiber sold by American Kynol, Inc., Altamonte Springs, Fla.), Pyron PW6(a polyacrylonitrile fiber sold by Stackpole Fibers Company, Inc.,Lowell, Mass.), and preferably VS-0050 (a pitch fiber sold by UnionCarbide Co., Greenville, S.C.) woven into an 8-harness weave is subjectto a pretreatment process that oxidizes and stablizes fiber surfaces.Generally, the process, which comprises an exposure of fibers in anoxidizing atmosphere to temperatures of about 260°-315° C., prevents thefibers from remelting during initial pyrolization and maintains fiberintegrity.

Impregnation of the fibers with a resinous material is accomplished byimmersing the cloth into resin-solvent admixture containing about 1 partresin such as BRP-5549 (a phenolic resin sold by Union Carbide Co., NewYork, N.Y.), K-700R (a furan resin sold by Fiberite Corp., Winona,Minn.), HA-43 (a polyphenylene resin sold by Hercules, Inc., Salt LakeCity, Utah), and preferably K-640 (a phenolic resin sold by FiberiteCorp., Winona, Minn.) to 1 part solvent, such as isopropyl alcohol. Theinclusion of the solvent in the resin-solvent admixture enhanced theeven dispersal of the resin on the cloth. As the solvent evaporated, theviscosity of the resin increased.

Impregnated cloth was spread on a smooth surface, such as a plasticsubstrate, and allowed to air dry. The dried cloth was cut into thedesired configuration and the plies were stacked one upon another, toform an uncured layup. For example, a stock of ten to twenty pliesproduced a layup about 1/8 to 1/4 inch thick.

The layup was cured by subjecting it to a curing temperature and amolding pressure cycle of about 165° C. over a rise time of one hour andholding such temperature for an additional hour at a pressure of 15-80psi (pounds per square inch) to form a cured laminate.

After the cured laminated part was packed in calcined coke in a retort,the retort was placed in a pyrolization furnace. The part was graduallybrought up to pyrolization temperature of about 815° C. over an extendedheating cycle which can vary in accordance with the materials and thenumber of plies for a particular part. Typically, a 72 hour cycle wasemployed, however, in some cases, longer periods, up to 14 days, wereemployed to obtain parts with somewhat greater physical integrity.Extended heating cycles were required for parts of larger size andgreater number of laminations and to ensure slow rates of release offiber and resin volatiles in order to prevent delamination of partscaused by excessively rapid volatile release.

Finally, the parts were heated to about 2000° C. for about 14 hours,held at about 2000° C. for about two additional hours, and graduallycooled by turning off furnace power.

Whereas organic fibrous precursors of multiple plies of woven clothproduced composites having two-dimensional strength characteristics, inanother embodiment of the present invention an analogous process wasemployed to form elongated bodies with unidirectional fibers havingenhanced longitudinal strength characteristics. The fibers were suppliedin the form of roving yarn, such as Kynol KR-0204 (a phenolic-basedfiber sold by American Kynol, Inc., Altamonte Springs, Fla.), Pyrol 30R(a polyacrylonitrile fiber sold by Stackpole Fibers Company, Inc.,Lowell, Mass.), Grafil 0 (a polyacrylonitrile fiber sold by Courtaulds,Ltd., Coventry, England) and preferably VS-0050 and VS-0061 (pitch-basedfibers sold by Union Carbide Company, Greenville, S.C.). The bodies areformed by the use of elongated, substantially bar shaped winding toolsupon which a yarn or roving of organic fibrous material was woundlongitudinally under tension.

Resin was applied to the fibers in a vacuum by pouring uncured resinover the layup. After removal from the vacuum chamber, the layup wasdried, and then cured, pyrolyzed, and heat treated in accordance withthe aforedescribed procedure yielding unidirectional bodies that aresuitable for use as elongated elements. Parts produced fromunistructural laminates are less porous then those produced from clothlaminates and exhibit flexure strength in excess of 50,000 psi.

In yet another embodiment of the present invention, the above-mentionedfibers were chopped into one-half inch lengths, fluffed in a blender athigh speed, and spread over a flat surface to form a fibrous mat. Themat was impregnated with a resin-solvent admixture and dried. The layupwas placed in a mold and cured at temperatures of about 165° C. inaccordance with the aforedescribed procedure. The cured laminate wasthen pyrolyzed and heat treated. The mat laminates were formed asrectangular structures about 1/4 inch in thickness, exhibiting goodthree-dimensional strength characteristics and flexure strengths ofabout 5,000 psi. In each of the embodiments of the present invention theuse of pitch fibers, the heat pretreatment of fibers prior to resinapplication, and the heat treatment of pyrolyzed bodies was found to bemost advantageous.

Futhermore, in every embodiment of the present invention the variablesof prepregging, B-staging, cure conditions of time, temperature and moldpressure were found to be interrelated and to influence resin flow whichaffects density, porosity, and structural soundness of composites.

Prepregging includes the physical layup of fibers, resin content, methodof applying resin to fibers, and method of drying. The general methodsof prepregging mat, cloth, and unistructure laminates are similar butwith differences in procedure. For mat laminate prepregging short piecesof fiber tow were fluffed in a blender and thoroughly mixed mechanicallywith the desired amount of resin-solvent admixture before being spreadout to dry. For cloth laminate prepregging the desired amount ofresin-solvent admixture was applied to cloth temporarily affixed to abase sheet to insure that the cloth was not pulled out of square duringprocessing and then turned over several times to allow both sides todry. For unistructure drum wound laminate prepregging the desired amountof resin-solvent admixture was applied onto fiber tow while being woundunder tension around a drum in a tight helix so that adjacent wrapstouched and then they were allowed to air dry. For unistructure tensionwound laminate prepregging the desired amount of resin-solvent admixturewas admitted into a vacuum desiccator to cover fiber tow wound undertension in successive layers onto a two bladded wheel followed by airdrying.

B-staging was only required for the K-640 phenolic resin system and wascarried out by placing the prepreg in a Blue M hot air oven for therequired amount of time.

Mold pressure applied during cure was usually changed during the curecycle which varied for each resin system. Included in some cure cyclesat 80° C. and again at 100° C. for a predetermined amount of time therewas a bump, an intentional momentary release of mold pressure to helprelease trapped cure gases. Generally, post cures performed underpressure were not completely successful except when much slowerpyrolysis cycles effectively incorporated a post cure into the firststage of the pyrolysis cycle.

Pyrolysis and post-pyrolysis heat treatment of laminates was broken downinto two or three successive cycles of temperature range and time. Majorweight loss and shrinkage and most of the cracking and delaminationsoccurred with pyrolysis to 800° C. Heat treatments in excess of 1500° C.caused an increase in fiber strength and modulus of pyrolyzed laminates.

Densification of pyrolyzed or heat treated laminates involvesreimpregnation with resin, cure, and repyrolysis. The process is used tohelp fill the extended open porosity developed during initial pyrolysis.It directly decreased porosity and increased density, strength, andmodulus.

The pieces of equipment used for pyrolization were: an electric furnacemade by K. H. Huppert Co., Type ST, Style 21 AHT, with a Barber-ColemanCam Controller, Model 2040-25240; and an electric furnace made byLindberg, box furnace Model 51662 and console Model 59554-S, capable of1100° C. with inert gas retort, controlled by a microprocessor fromResearch Inc., MicRIcon Model 82300. Some cloth laminates were pyrolyzedin a fast 2 hour cycle in a Marshall tube furnace, Model 1442 made byNorton, Vacuum Equipment Div., but for slower cycles an electric furnacemade by Sybron Corp., Thermolyne Type 1500, Model FDI520M-1, was used to500°-600° C. followed by further pyrolysis to above 800° C. in theHuppert furnace. Heat treatments to 2000° C. in 16 hour cycles were runin an Astro 1000-3060 furnace made by Astro Industries, Inc., SantaBarbara, Calif.

The invention is illustrated by the following examples.

EXAMPLE I

A plurality of VS-0050 pitch fiber mat buttons pretreated either byexposure to an oxidizing atmosphere maintained at a temperature of 300°C. for 3 hours or at a temperature in excess of 400° C. were saturatedwith a 33-50% by wt. BRP-5549 resin-isopropyl alcohol admixture. Thebuttons were subjected to a cure cycle with a rise time of 40 minutes to180° C. or a rise time of 140 minutes to 180° C. and cure pressures of200-1000 psi. Some of the buttons were subjected to a postcure treatmentof a 3 day cycle to 260° C., while others did not undergo any postcuretreatment whatsoever. The buttons were then pyrolyzed using a 72 hourcycle to 816° C. Evaluation of the data indicated that (a) higher resincontent and higher cure pressures produced denser, less porouslaminates, but with more and worse cracks after pyrolysis, and (b) fiberprechar produced porous, less dense laminates.

EXAMPLE II

A plurality of VS-0050 pitch fiber mat laminates some of which were notpretreated while others were pretreated by exposure to an oxidizingatmosphere maintained at a temperature of 300°-315° C. for 3 hours weresaturated with a 40-60% by wt BRP-5549 resin-isopropyl alcohol admixtureor with a 40-50% by wt K-640 resin-isopropyl alcohol admixture. Thelaminates were sdbjected to a cure cycle with a rise time of 75 minutesto 150° C., or a rise time of 115 minutes to 175° C., or a rise time of90 minutes to 160° C., or a rise time of 120 minutes to 163° C., or arise time of 140 minutes to 163° C., and cure pressures of 30-1500 psi.Some of the laminates were subjected to a post cure treatment of a 3 daycycle to 260° C., while others did not undergo any post cure treatmentwhatsoever. The laminates were then pyrolized using a 72 hour cycle to816° C., or a 374 hour cycle to 663° C., or a 240 hour cycle to 538° C.Some laminates were subjected to a post pyrolysis treatment of a 12 hourcycle to 2000° C., while some laminates were subjected to densification.Evaluation of the data indicated that (a) lower cure pressures producedporous laminates without cracks after pyrolysis but with lower flexurestrength and modulus, (b) additional heat treatment produced laminateswith increased flexure strength, and (c) densification producedlaminates with less than expected improvement in flexure strength.

EXAMPLE III

A plurality of Grafil 0 fiber, or VS-0050 or VS-0061 pitch fiber matcomposites some of which were prepyrolyzed using a 72 hour cycle to 816°C. while others were pretreated by exposure to an oxidizing atmospheremaintained at a temperature of 300° C. for 3 hours were saturated with a40-50% by wt K-640 resin-isopropyl alcohol admixture or with a 50% by wtHA-43 resin-isopropyl alcohol admixture. The laminates were subjected toa cure cycle with a rise time of 120 minutes to 163° C., or a rise timeof 140 minutes to 163° C., or a rise time of 40 minutes to 150° C. andcure pressures of 18-2000 psi. Some of the laminates were subjected to apost cure treatment of a 3 day cycle to 220° C., while others did notundergo any post cure treatment whatsoever. The laminates were thenpyrolyzed using a 72 hour cycle to 816° C., or a 374 hour cycle to 663°C., or a 382 hour cycle to 820° C., or a 329 hour cycle to greater than1100° C., or 365 hour cycle to 748° C. Some of the laminates weresubjected to a post pyrolysis treatment of a 7 hour cycle to 1677° C.,or a 12 hour cycle to 2000° C., or a 16 hour cycle to 2000° C. One ofthe VS-0050 pitch fiber composites was saturated with a 50% by wt K-640resin and 5% by wt graphite powder-isopropyl alcohol admixture.Evaluation of the data indicated that (a) slower pyrolysis cyclesreduced but did not eliminate blistering and spalling of Grafil-0 fiberlaminates, (b) laminates of prepyrolyzed Grafil-0 fibers were porousafter curing and after pyrolysis, (c) heat treatment of pyrolyzedGrafil-0 fiber laminates increased flexure strength, (d) intactpyrolyzed laminates exhibited significant strength increase with heattreatment, and (e) method used to mold mat laminates effected their bulkdensities and flexural strength.

EXAMPLE IV

A plurality of Pyron PW6 fiber, or Kynol 2400 fiber cloth buttonspretreated by exposure to an oxidizing atmosphere maintained at atemperature of 300° C. for 3 hours, or pretreated by exposure to anoxidizing atmosphere maintained at a temperature of 206° C. for 5 hours,or charred at a temperature about 400° C. were saturated with a 30-60%by wt BRP-5549 resin-isopropyl alcohol admixture or with a 40% by wtK-640 resin-isopropyl alcohol admixture. The cloth buttons weresubjected to a cure cycle with a rise time of 90 minutes to 130° C., ora rise time of 70 minutes to 150° C., or a rise time of 80 minutes to150° C., or a rise time of 90 minutes to 180° C., or a rise time of 120minutes to 180° C. and cure pressures of 200-1000 psi. The cloth buttonswere then pyrolyzed using a 72 hour cycle to 816° C. Evaluation of thedata indicated that (a) Pyron PW6 cloth buttons blistered anddelaminated during prolysis, (b) Pyron PW6 fiber pretreated by charringproduced low density, solid, intact cloth buttons, and (c) pretreatedKynol 2400 fiber produced satisfactory pyrolyzed buttons.

EXAMPLE V

A plurality of Pyron PW6 fiber, or Kynol 2400 fiber cloth swatchlaminates some of which were not pretreated while others were pretreatedby charring at 484° C. were saturated with a 40-60% by wt K-640resin-isopropyl alcohol admixture. The cloth laminates were subjected toa cure cycle with a rise time of 90 minutes to 160° C. and curepressures of 16-400 psi. The cloth laminates were then pyrolyzed using a72 hour cycle to 816° C., or a 2 hour cycle to 827° C. Evaluation of thedata indicated that (a) Pyron cloth laminates subjected to the fasterpyrolysis rate were slightly less dense, and (b) Pyron precharred fiberwith higher resin content produced laminates that were denser as cured,but less dense after pyrolysis than previous swatch laminates.

EXAMPLE VI

A plurality of Pyron PW6 fiber, or Kynol 2400 fiber cloth laminates someof which were not pretreated while others were pretreated by exposure toan oxidizing atmosphere maintained at a temperature of 206°-318° C. for5 hours, or by charring at 296°-437° C. were saturated with a 40-60% bywt K-640 resin-isopropyl alcohol admixture. The cloth laminates weresubjected to a cure cycle with a rise time of 90 minutes to 160° C., ora rise time of 140 minutes to 163° C. and cure pressures of 15-30 psi.The cloth laminates were then pyrolyzed using a 72 hour cycle to 816° C.Some of the pyrolyzed cloth laminates were subjected to a densificationprocess whereby the laminates were reimpregnated with K-640 resinadmixture, recured, and repyrolyzed. Evaluation of the data indicatedthat (a) densification increased density, decreased porosity, andimproved flexure strength of Pyron PW6 laminates, and (b) densificationdecreased flexure strength of Kynol 2400 laminates.

EXAMPLE VII

A plurality of Pyron PW6 fiber, or Kynol 2400 fiber cloth laminates someof which were not pretreated while others were pretreated by exposure toan oxidizing atmosphere maintained at a temperature of 260° C. for 5hours. or by charring at 296°-437° C. were saturated with a 60% by wtK-640 resin-isopropyl alcohol admixture. The cloth laminates weresubjected to a cure cycle with a rise time of 90 minutes to 160° C., ora rise time of 140 minutes to 163° C. and cure pressures of 30 psi. Thecloth laminates were then pyrolyzed using a 72 hour cycle to 816° C.Some of the pyrolyzed cloth laminates were densified by reimpregnationwith the K-640 resin admixture and repyrolyzed using a 15 hour cycle to1016° C. Evaluation of the data indicated that (a) cure and pyrolysisdensities of laminates increased, (b) densification increased density,decreased porosity, (c) densification slightly increased flexurestrength, and (d) bulk densities were higher and apparent porositieswere lower compared to laminates of Example VI.

EXAMPLE VIII

A plurality of VS-0050 pitch fiber cloth laminates pretreated byexposure to an oxidizing atmosphere maintained at a temperature of 300°C. for 3 hours were saturated with a 40-60% by wt K-640 resin-isopropylalcohol admixture. The cloth laminates were subjected to a cure cyclewith a rise time of 120 minutes to 163° C., or a rise time of 140minutes to 163° C. and cure pressures of 18-400 psi. The cloth laminateswere then pyrolyzed using a 72 hour cycle to 816° C., or a 240 hourcycle to 538° C., or a 382 hour cycle to 820° C., or a 329 hour cycle togreater than 1100° C. Some of the pyrolyzed cloth laminates were furtherheat treated using a 7 hour cycle to 1677° C., or a 12 hour cycle to2000° C., or a 16 hour cycle to 2000° C. Evaluation of the dataindicated that (a) heat treatment produced laminates with increasedflexure strength and bulk density.

EXAMPLE IX

A plurality of VS-0050 pitch fiber cloth laminates pretreated byexposure to an oxidixing atmosphere maintained at a temperature of 300°C. for 3 hours were saturated with either a 40-50% by wt K-640resin-isopropyl alcohol admixture, or a 40% by wt K-640 resin and 5% bywt graphite powder-isopropyl alcohol admixture, or 57% by wt K-700Rresin-isopropyl alcohol admixture, or 50% by wt HA-43 resin-isopropylalcohol admixture. The cloth laminates were subjected to a cure cyclewith a rise time of 120 minutes to 163° C., or a rise time of 37 minutesto 150° C. and cure pressures of 18-80 psi. Some of the cloth laminateswere then pyrolyzed using a 72 hour cycle to 816° C., or a 309 hourcycle to 850° C., or a 329 hour cycle to greater than 1100° C. Some ofthe pyrolyzed cloth laminates were further heat treated using a 16 hourcycle to 2000° C. Evaluation of the data indicated that flexure strengthof the cloth laminates significantly increased with heat treatments.Some of the heat treated, pyrolyzed cloth laminates were densified byreimpregnation with 40% by wt. K-640 resin-isopropyl alcohol admixtureand pyrolyzed using a 72 hour cycle to 816° C.; some of the oncedensified cloth laminates were again densified by reimpregnation with50% by wt K-640 resin-isopropyl alcohol admixture and pyrolyzed using a72 hour cycle to 816° C.; and some of the twice densified clothlaminates were again densified by reimpregnation with 50% by wt K-640resin-isopropyl alcohol admixture. Evaluation of the data indicated that(a) flexure strength of the cloth laminates significantly increased withheat treatment and densification.

EXAMPLE X

A plurality of VS-0050 and VS-0061 pitch fiber unistructure yarnlaminates pretreated by exposure to an oxidizing atmosphere maintainedat a temperature of 300° C. for 3 hours were saturated with either 57%by wt. K-700R resin-isopropyl alcohol admixture or a 50% by wt. HA-43resin-isopropyl alcohol admixture, or a 40% by wt. K-640 resin-isopropylalcohol admixture. The unistructure yarn laminates were subjected to acure cycle with a rise time of 120 minutes to 163° C., or a rise time of37 minutes to 150° C. and cure pressures of 18-80 psi. The unistructureyarn laminates were then pyrolyzed using a 72 hour cycle to 816° C., ora 309 hour cycle to 850° C., or a 329 hour cycle to greater than 1100°C. The pyrolyzed yarn laminates were further heat treated using a 16hour cycle to 2000° C. Evaluation of the data indicated thatsignificantly high flexure strengths were obtained from the unistructurefiber laminates without densification. Evaluation of the data alsoindicated that flexure strength of the unistructure fiber laminatessignificantly increased with heat treatments.

While the within invention has been described as required by law inconnection with certain preferred embodiments thereof, it is to beunderstood that the foregoing particularization and detail have been forthe purposes of description and illustration only and do not in any waylimit the scope of the invention as it is more precisely defined in thesubjointed claims.

What is claimed is:
 1. A method for forming structural carbon-carboncomposites, which comprises:pretreating an organic fibrous precursor byexposure for about three hours to an oxidizing atmosphere maintained ata temperature range of 260°-315° C.; impregnating the fibrous precursorwith a matrix-forming resinous binder admixed with a solvent material;composing an assemblage of the resinous binder impregnated fibrousprecursor cut to form a composite layup of predetermined configuration;subjecting the composite layup to a curing temperature and moldingpressure cycle of about 165° C. over a rise time of about one hour and aholding time of about one hour at a pressure range of 15-80 psi to forma cured laminate; pyrolyzing the cured laminate in a pyrolizationfurnace by gradually raising the furnace temperature to about 815° C.over a heating cycle of 72-336 hours to form a pyrolyzed laminate; andheat treating the pyrolyzed laminate over a heating cycle of about 14hours to a temperature of about 2000° C. and maintaining suchtemperature for about two additional hours followed by a gradual coolingof heat treated laminate to ambient temperature.
 2. The method asrecited in claim 1, wherein the organic fibrous precursor is selectedfrom the group consisting of polyacrylonitrile, and phenolic.
 3. Themethod as recited in claim 1, wherein the resinous binder is selectedfrom the group consisting of polyphenylene resin, phenolic resin andfuran resin.
 4. The method as recited in claim 1, wherein the solventmaterial is selected from the group consisting of isopropyl alcohol andmethyl ethyl ketone.
 5. A method for forming structural carbon-carboncomposites, which comprises:pretreating woven cloth of organic fibrousmaterial by exposure for about three hours to an oxidizing atmospheremaintained at a temperature range of 260°-315° C.; impregnating thefibrous material with a matrix-forming resinous binder admixed with asolvent material; composing one upon another a plurality of plies of theresinous binder impregnated fibrous material cut to form a compositelayup of predetermined configuration; subjecting the composite layup toa curing temperature and molding pressure cycle of about 165° C. over arise time of about one hour and a holding time of about one hour at apressure range of 15-80 psi to form a cured laminate; pyrolyzing thecured laminate in a pyrolization furnace by gradually raising thefurnace temperature to about 815° C. over a heating cycle of 72-336hours to form a pyrolyzed laminate; and heat treating the pyrolyzedlaminate over a heating cycle of about 14 hours to a temperature ofabout 2000° C. and maintaining such temperature for about two additionalhours followed by a gradual cooling of the heat treated laminate toambient temperature.
 6. The method as recited in claim 5, wherein theorganic fibrous material is preferably pitch fibers woven into cloth. 7.A method for forming structural carbon-carbon composites, whichcomprises:pretreating organic fibrous material by exposure for aboutthree hours to an oxidizing atmosphere maintained at a temperature of260°-315° C.; composing a layered mat of the fibrous material shaped toform a composite layup of predetermined configuration; impregnating thecomposite layup with a matrix-forming resinous binder admixed with asolvent material; subjecting the composite layup to a curing temperatureand molding pressure cycle of about 180° C. over a rise time range of40-140 minutes at a pressure range of 200-1000 psi to form a curedlaminate; pyrolyzing the cured laminate in a pyrolization furnace bygradually raising the furnace temperature to about 815° C. over ahealing cycle of 72-382 hours to form a pyrolyzed laminate; and heattreating the pyrolyzed laminate over a heating cycle of about 14 hoursto a temperature of about 2000° C. and maintaining such temperature forabout two additional hours followed by a gradual cooling of the heattreated laminate to ambient temperature.
 8. The method as recited inclaim 7, wherein the layered mat consists of organic fibrous materialchopped in one-half inch lengths and fluffed in a blender at high speed.9. A method for forming structural carbon-carbon composites, whichcomprises:pretreating elongated bodies of unidirectional organic fibrousmaterial by exposure for about three hours to an oxidizing atmospheremaintained at a temperature range of 260°-315° C.; impregnating thefibrous material with a matrix-forming resinous binder admixed with asolvent material; composing one upon another a plurality of plies of theresinous binder impregnated, parallel oriented fibrous material cut toform a composite layup of predetermined configuration; subjecting thecomposite layup to a curing temperature and molding pressure cycle ofabout 165° C. over a rise time of about one hour and a holding time ofabout one hour at a pressure range of 15-80 psi to form a curedlaminate; pyrolyzing the cured laminate in a pyrolization furnace bygradually raising the furnace temperature to about 815° C. over aheating cycle of 72 hours to form a pyrolyzed laminate; and heattreating the pyrolyzed laminate over a heating cycle of about 14 hoursto a temperature of about 2000° C. and maintaining such temperature forabout two additional hours followed by a gradual cooling of the heattreated laminate to ambient temperature.
 10. The method as recited inclaim 9, wherein the elongated bodies of unidirectional organic fibrousmaterial are wound under tension around a drum.
 11. The method asrecited in claim 9, wherein the elongated bodies of unidirectionalorganic fibrous material are wound under tension in successive layersonto a two bladed wheel.
 12. The method as recited in claim 9, whereinthe elongated bodies of unidirectional organic fibrous material areimpregnated in a vacuum chamber with the matrix-forming resinous binder.